This invention relates to a system and method that non-intrusively monitor and report on the condition and performance of electrochemical batteries used in vehicles.
The primary purpose of batteries used in internal combustion powered vehicles is to provide energy for starting, lighting and ignition (SLI), and accordingly, they are referred to as SLI batteries. The secondary purpose of such batteries is to provide energy during periods when a vehicle""s electrical energy generation (alternator and its regulator) system cannot temporarily sustain the electrical load. Batteries invariably do not lose the ability to perform their functions or fail instantaneously. Loss of capability or the inability of a battery to provide electrical energy results from various degrading factors, several of which are described below.
Batteries, regardless of type (e.g., thin plate SLI (Starting-Lighting-Ignition) or thick plate (Storage or Traction), or electro-chemistry system, e.g., Lead-Acid, Nickel-Cadmium NiCd, Nickel Metal Hydride, Lithium-Ion, etc., share the common characteristics of loss of capability to perform their normal functions. No single measured parameter is available to indicate battery performance capability.
Battery performance capabilities continuously vary. Temperature, electrolyte and plate condition and SoC (State-of-Charge) are among the primary influencing factors. Battery internal resistance (IR), polarization resistance (PR) and SoC, have been used as sources of information for providing real-time reporting of battery conditions and performance capabilities. For example, it is known that the maximum instantaneous power that a battery can output is inversely proportional to its internal resistance. Battery polarization resistance PR, which arises from non-uniformity in electrolyte concentration at the battery plates, affects the power output in a somewhat similar manner. Two systems for indicating certain aspects of battery capability and a few possible fault conditions are described in U.S. Pat. No. 4,937,528, entitled xe2x80x9cMethod For Monitoring Aircraft Battery Statusxe2x80x9d and U.S. Pat. No. 5,281,919, entitled xe2x80x9cAutomotive Battery Status Monitorxe2x80x9d.
A battery having assured performance capability requires a high SoC and high capacity, usually measured in Amp/hours, plus low dynamic internal resistance (IR). As used herein, the term xe2x80x9cdynamic IRxe2x80x9d means the battery IR (internal resistance) measured when an installed battery discharges current to a large load, such as a starter motor during engine cranking.
Terminal voltage or electrolyte gravimetric measurements have been used to indicate state-of-charge (SoC). Battery capacity measurement typically involves employing a shop or laboratory tester and use of procedures that require measurement of total discharge followed by the measurement of total re-charge.
Static IR is generally used to verify design and quality consistency and assurance. Methods for static IR measurement require charging a battery to the maximum state-of-charge (SoC) as determined when the maximum terminal voltage is achieved. Following charging to maximum SoC, a battery is subjected to a series of increasing loads for specific time periods. During these programmed discharges, current and voltage are monitored and internal resistance values are computed and plotted. The plotted data indicates the static IR. Such tests may also be performed at various temperatures and various levels of SoC. Dynamic IR also indicates quality but, more important, it has been found to be a predictor of the battery""s ability to meet a vehicle""s demand under high load conditions, such as engine starting, over the expected range of temperature at which the battery is to operate.
Battery capacity and IR (both static and dynamic) undergo changes. No two batteries may necessarily have identical values. Battery plate conditions, including both the plate surface and the usefulness of the active plate material, constantly change. An electrochemical system loses capacity when effective plate area is reduced by such conditions as sulfation for a lead-acid battery or memory effect for a NiCd battery. These effects are well known.
All re-chargeable batteries can sustain many discharge-recharge cycles. The number of cycles is influenced by the rate at which the plates deteriorate. The reasons for and duration of the deterioration are influenced by such use conditions as ambient temperatures, magnitude and duration of the load, low SoC durations, vibration and other cyclical effects. Catastrophic conditions occasionally occur. For example, short circuits cause extremely large discharges which produce rapid and large rises in plate temperatures that cause plate warping along with active material loss.
SLI batteries have thin and very porous plates. Batteries designed for continuous duty for periods between re-charging have thick plates. The thin plates in SLI batteries provide large current out-rushes at the beginning of vehicle engine cranking. At low temperature conditions, a typical 5-liter engine frequently draws 1600 or more Amperes during engine cranking. This large battery current out-rush or drain during cranking, lasts for around 10 milliseconds or less depending on many factors. The large current drain continues at a declining rate during cranking. This is shown in FIG. 6 (described in detail below), which depicts voltage (across the battery terminals) and current waveform curves during engine cranking. Engine cranking is usually limited to 2 engine revolutions for modern, sequential fuel injected engines. Reasons for limiting engine revolutions include avoiding the production of unnecessary hydrocarbon emissions, damaging the vehicle""s catalytic converter, starter motor over-heating and the possibility for battery plate-warping.
The voltage and current curves, depicted in FIG. 6, provide the dynamic bases for determining battery dynamic internal resistance (IR) and polarization (PR). The IR and PR of batteries for electric and hybrid vehicles are determined in a like manner.
The SoC of a battery is generally defined as the percentage of battery charge capacity available relative to the rated battery capacity at that time. In an SLI (lead-acid) battery, as the SoC increases from 80% to 95%, the conversion efficiency of the battery from electrical (charge input) to chemical conversion by the battery declines from 99% to 95% or less. Above 92% SoC, SLI batteries are more prone to generating Hydrogenxe2x80x94electrolysis. This phenomenon causes electrolyte depletion and a potentially hazardous condition. To minimize these possible conditions, voltage regulators in internal combustion engine powered vehicles generally limit the charge of an SLI battery SoC to approximately 92%. The voltage regulators limit SoC by controlling the alternator output voltage. Since SoC is influenced by ambient temperature, voltage regulators employ temperature-varying resistors. This technique enables adjustment of the alternator output voltage used to charge the battery to accommodate .for high electrolyte activity in high ambient temperature environments and for a low activity level during low ambient temperatures.
Usually an alternator provides all of the vehicle""s electric energy requirements during normal operation. However, high and low ambient temperatures frequently cause loads that exceed an alternator""s capacity. Also, demands on alternators may exceed their capabilities with the ever increasing complement of OEM (Original Equipment Manufacturer) equipment in the vehicle and after-market devices, such as extra high intensity lighting, communications devices, computers and other electric energy consumers.
During periods of high ambient temperature and the consequential battery high electrolyte activity, corrosion of the battery plates becomes a possible cause for battery failure. The problem becomes more severe when operation is at night in a high temperature and high humidity environment for short periods that do not allow for the restoration of the battery charge by the alternator. Extremely cold ambient conditions at night, where electrolyte activity is low and opportunities to recharge may be fewer, are also causes for battery failure.
Charging system (alternator and regulator) failures or even partial reduction of their output capabilities often cause battery deterioration and at times unanticipated loss of operation. Present methods and apparatus directed towards mitigating these problems are limited. No means are currently known to be available which indicate all of the limitations of battery capability, on-going deterioration or other problems as discussed above. Limited means employed in the past were generally costly and intrusive.
Accordingly, a need exists to provide a system and method to monitor, or diagnose, the conditions of a vehicle battery on a real-time, non-intrusive basis, to monitor the vehicle alternator and regulator, and to predict battery performance and life.
The present invention relates to a system and method for use with a vehicle battery, and particularly one used for SLI purposes. This invention is also applicable to both battery powered and hybrid vehicles, i.e., those which employ both internal combustion engines and batteries. The system and method of the invention effect real-time determination and notification to the vehicle user of battery state-of-charge (SoC), engine start alert capability, battery reserve capacity (in time units) and other factors, such as electrolyte depletion, on-going connector loosening (loss of xe2x80x9cgas-tightxe2x80x9d integrity) which in turn leads to corrosion, charging system (alternator and regulator) deterioration and failure, and electric energy deficits.
To assure performance veracity, the system and method employ re-calibration and updating techniques on a database of measured quantities. From this data, calculation of dynamic IR and dynamic PR is made, as well as an evaluation of the trends of increase or decrease of these factors and of battery SoC and capacity.
The present invention is a system and process implemented with a computer or similar equipment complemented with attached voltage, temperature and current sensing means that:
(a) continuously monitor ambient temperature, battery terminal voltage and current flow (i.e., charge and discharge) into and out of a battery in a vehicle,
(b) dynamically determine internal resistance (IR) and polarization resistance (PR) during servicing of large energy demands such as engine starting,
(c) construct databases stored in the computer memory, such as a partially permanent memory (e.g., electronically alterable read-only-memory EARPROM) for determining battery condition and capability,
(d) accept and then store in the data base 1) vehicle data and battery data provided by the manufacturer, 2) vehicle electric load data, and 3) vehicle starting current data, such as included and used for SoC vs. IR, IR vs. Temperature,
(e) acquire, accumulate and store vehicle and battery experience data,
(f) adjust initially stored data using the experience data and store data revisions in the database,
(g) compute condition trends for indicating current and future battery operation conditions,
(h) use IR as corrected by battery temperature correction data with required IR vs. Temperature data to compute the lowest possible temperature at which the battery can start the engine (Limit),
(i) continuously compute and update SoC as the result of recent and on-going discharge and charge experience as corrected by ambient conditions,
(j ) transmit advisories and condition reports to discrete or program displays and to other vehicle systems for electric load management,
(k) report diminishing battery reserve capacity, in minutes or other appropriate time units, when a vehicle is idle (engine not running for internal combustion engine powered vehicles) or a charging system failure, such as a broken alternator belt, faulty regulator or defective alternator,
(l) during engine non-operation (i.e., Sleep Mode), provide condition reserve capacity advisories that indicate the time remaining before a battery loses its capability for starting the engine. Advisories during engine operation, or xe2x80x9cRun Modexe2x80x9d, indicate the time remaining before a battery loses capability for supporting operation of the vehicle electrical system. This is useful because internal combustion engines depend on electric power for fuel pumping, ignition, fuel injection, control and so forth, and
(m) when applicable, provide access to a database through a vehicle""s diagnostic connector.
Although the invention is described relative to lead-acid battery technology which is usually employed in SLI and other vehicle batteries, the invention is applicable to other technologies, such as nickel metal hydride, and lithium ion. These batteries are further classified according to their construction: flooded cells, maintenance-free and sealed. This invention is applicable to any internal combustion engine powered vehicle with integral means for battery charge maintenance that transport or convey people, or material. Cars, trucks, boats, aircraft, agricultural and construction equipment and industrial prime movers (e.g., fork lifts, cranes) are examples. This invention is also applicable to hybrid vehicles, which employ both internal combustion engines and batteries for vehicle powering. Parts of this invention also are applicable to electric, battery-powered vehicles and hybrid vehicles.
It is an object of the invention to provide a method and system for continuously determining the condition of a vehicle battery and its capability.
Another object is to provide a method and system for continuously monitoring voltage and current responses of a vehicle battery to update a database that determines battery condition and capability, including its state-of-charge (SoC) and trends in conditions, such as depleting electrolyte, lose of capacity and other such pending failures.
A further object is to monitor, determine and indicate the condition of the associated alternator, regulator and drive components associated with a vehicle battery.
Yet another object is to provide a system and method for monitoring a vehicle battery and determining its reserve capacity relative to its ability to be able to start the vehicle engine.
An additional object is to provide a system and method that compute the lowest possible temperature at which a vehicle""s battery is able to start the engine.